The invention relates to a method for determining values influencing the movement of a robot, in particular to a method for planning and evaluating production plants that are operated in the sense of a human-robot collaboration.
When a human being and a robot are intended to work in close collaboration, it is important to know the risk posed to the person by the robot at all times.
There are currently approaches for assessing already existing plants in terms of the risk posed to humans, such as the calculation models or collision measurements in the production plant disclosed in DE 10 2013 212 887 A1. Accordingly, potential human and robot collision sites are identified and assessed in terms of their risk in accordance with specified standards (for example, ISO10218-1, ISO10218-2, TS 15066, BG/BGIA Recommendation for Risk Assessment According to the Machinery Directive—Designing of Workplaces with Collaborating Robots—U001/2009). If the risk is too high, appropriate adjustments are made to the movement or rather the path and/or to the speed of the robot. This is carried out in an iterative manner until all risks have been eliminated. These kinds of methods are not only very laborious but also require a physically existing facility or plant in every case. Furthermore, these methods only work if the robot dynamics model is precisely known, which is often not the case is in actual practice. Furthermore, the computer model must be set up anew and revalidated for every change in the hardware or software.
Because the collision behavior cannot be calculated exactly with these methods, the movements must be executed in perhaps extreme slow motion, which can lead to reduced cycle times. Furthermore, reproducibility or repeatability is difficult with measurements in the actual plant. Also, it is not possible to take measurements at each point in a given plant at the present time because the measurement systems used for taking measurements cannot be mounted on every site in a given plant on account of interfering contours.
The problem addressed by this invention is therefore that of providing a coherent approach by means of which the risk to a human being can be assessed in the planning, stage so that appropriate changes can also be made at this stage.
The method of the invention for determining values influencing the movement of a robot comprises the following steps:
a) Provision of a task to be performed by the robot and a worker;
b) Provision of a layout of a workstation in which the task shall be performed;
c) Provision of tool data that characterize a tool that the robot shall use in performing the task;
d) Determination of respective axial movement patterns, which are required for performing the task, of the robot on the basis of the information provided in the preceding steps;
e) Provision of a workspace for the worker;
f) Determination of relevant, in particular critical path points of the robot, in particular within the worker's workspace, at which a predefined movement speed will be exceeded by the robot and/or at which a predetermined mass of an element to be moved by means of the robot will be exceeded, on the basis of the axial movement patterns and the workspace;
g) Simulation of respective collisions at the path points by means of a second robot;
h) Determination of permissible operating speeds of the robot for any given, preferably critical path point on the basis of the simulated collisions.
The aforementioned problem is thus inventively solved in that the collision forces and surface pressures actually arising in the operation are determined with the aid of a test structure consisting of an industrial robot that simulates an unyielding impact in any given position of the workspace. In this manner the maximum operating speed can be determined for each point of the robot's trajectory during the planning stage. In contrast to the aforementioned prior art approach, an evaluation can thus be performed on the basis of all effects resulting from the robot movement.
These effects are primarily speeds, masses, geometries, distances, accessibility by body parts, the strategy used to control the movement, protective elements used, and material properties.
This approach is essential for determining whether a plant fulfills current BG recommendations and standards; i.e., whether there are any risks according to ISO 10218-2. With the method of the invention, a plant intended to be operated in the sense of a human-robot collaboration can be planned in a particularly rational manner. With the method of the invention, in particular it is possible to evaluate potential risks posed by the robot before constructing the actual plant.
An advantageous embodiment of the invention makes provision such that an enveloping space that surrounds the entire tool is established on the basis of the tool data. In other words, provision can be made of a so-called gripper envelope that takes the geometry of the tool concerned into account for possible collisions. This enveloping space is quickly and economically producible by means of, for example, a rapid prototyping process.
In another advantageous design of the invention, provision is made such that the axial movement patterns are determined by means of a simulation or a measurement. In the case of a simulation, the advantage lies in that the robot concerned does not need to be operated at all. The advantage of a measurement lies in that more precise axial movement patterns could be determined than with a simulation.
The simulation can be performed with a so-called office PC or with an RCS module or with any other path-accurate simulation option. This approach is particularly necessary in cases where the process has to be used in a tendering or planning phase.
According to another advantageous embodiment of the invention, provision is made such that potential crushing or pinning points, particularly within the worker's workspace, are determined on the basis of the axial movement patterns, at which points respective minimum distances between the production plant and the robot, as standardized in DIN EN 349, are not maintained. Potential risks posed to the worker while carrying out the specified work order can thus be determined at an early stage.
It is thus possible to depict the states of the robot in which security measures are required to protect all relevant body parts from pinning/crushing hazards as well as the states in which security measures are required to protect all relevant body parts from impact hazards.
Another advantageous embodiment of the invention makes provision such that a temporal progression of the reflected masses of the robot is determined. A reflected mass, a.k.a. a load mass, is the perceived mass of a module on a motor drive shaft of a drive motor; in this case the respective mass perceived on the axes of the robot. The actual masses to which the robot or worker will be subjected can thus be determined in a relatively reliable manner.
The mass/inertia properties of the robot and its limbs as well as the tool/workpiece properties are factored into the mass calculations.
In another advantageous design of the invention, provision is made such that the collisions simulated by means of the second robot are iteratively repeated by means of a pendulum and a load cell with different operating speeds until corresponding collision forces, collision pressures, and surface pressures are no longer reaching respective threshold values at the critical path points. Biomechanical load limits, which are specified by corresponding standards, for example, can thus be determined in a particularly reliable manner. In other words, so-called biofidelic load limits can be monitored and the corresponding operating speeds of the robot can be iteratively adjusted until accordingly specified threshold values are no longer being exceeded. Another advantageous embodiment of the invention makes provision such that a biofidelic test piece according to BG/BGIA recommendations is used as a mechanism for measuring force or pressure. Thus the biomechanics can thus also be depicted upon the impact of the robot and the test piece with each other.
The measurement of force and surface pressure could also be carried out on a process-steady measurement setup and by converting the recorded force progression to a progression that would have arisen on any spring-damper model. The conversion to the spring-damper models would advantageously be as specified in the standards for the various body parts.
Lastly, in another advantageous design of the invention provision is made such that for determining the respective collisions, the second robot is set in such a way that it simulates corresponding impact directions and resistances for the critical path points. Essentially any impact incidents can thus be simulated in a particularly precise, reproducible, and verifiable manner without any hardware modification.
Since the biomechanical load limits will also be exceeded in the effective direction of relevant geometries on the tool, there is a risk of impacts and pinning in this direction as well.
Other advantages, features, and details of the invention will emerge from the following description of a preferred exemplary embodiment and by referring to the drawings. The features and feature combinations mentioned in the preceding description as well as the features and feature combinations mentioned in the following description of the figures and/or shown in just the figures can not only be used in each specified combination but also in other combinations or by themselves, without exceeding the scope of the invention.